This invention relates to an absorption machine and, more particularly, to a variable effect desorber-resorber absorption heat pump/refrigeration machine utilizing two generators, two absorbers, a condenser, an evaporator and an intermediate desorber/resorber pair.
Single effect absorption refrigeration systems are well known in the art. In a typical single effect absorption system water is generally the refrigerant and lithium bromide is generally the absorbent, and together they are called a solution pair. Some systems employ high temperature solution pairs that are capable of operating at higher generator temperatures to increase efficiency but are precluded from operating at lower evaporator temperatures due to the possibility of freezing and crystallization of the refrigerant, while other chemical systems capable of operating at lower evaporator temperatures, even temperatures below the freezing point of water, could not operate at the higher generator temperatures, which are a consequence of the lower evaporator temperature, without stability problems. Consequently, a single effect system is generally limited in the selection of higher and lower operating temperatures in the generator and evaporator.
Absorption cycles of a single effect type generally comprise a generator for heating a weak or relatively dilute absorbent solution to generate both a vapor of refrigerant and a strong or relatively concentrated absorbent solution, a condenser for condensing the vapor of refrigerant, an evaporator for evaporating the condensed refrigerant to provide cooling, and an absorber for absorbing the refrigerant vapor from the evaporator into the strong absorbent solution to form a weak solution. However, the thermal efficiency (coefficient of performance or COP) of a single effect type absorption system is relatively low and ordinarily about 0.6-0.8. Accordingly, with a view toward increasing the thermal efficiency of absorption cycles, two stage generator type absorption units have been developed in which a further low side generator and condenser are additionally provided in the single effect type absorption refrigerator such that the high temperature vapor of refrigerant generated in a first high side generator is utilized to heat a second or low side generator. In general, a two stage generator type absorption unit comprises a high temperature generator, a low temperature generator, a high and low temperature condenser, an evaporator, an absorber, a high temperature heat exchanger and a low temperature heat exchanger. In the high temperature generator, a refrigerant dissolved in a solution, such as an aqueous solution of lithium bromide, is heated by heating means to discharge the dissolved refrigerant as vapor. Further, in one configuration, the discharged refrigerant vapor is fed through a heat transfer tube bundle to the low temperature generator to heat the weak solution supplied from the absorber, and while the refrigerant in the weak solution is discharged therefrom as vapor, the vapor from the strong solution is cooled by the latent heat of evaporation and nearly all is condensed prior to entering the condenser. The refrigerant vapor produced in the low temperature generator is supplied to the condenser and cooled by cooling means thereof and then condensed. This condensed refrigerant is generally sprayed into the evaporator thereby cooling the fluid means which cools a load. Moreover, the solution concentrated by discharging the refrigerant vapor in the high temperature generator is fed to the high temperature heat exchanger in heat exchange relation with the low temperature weak solution supplied from the low temperature generator, thereby suitably lowering its temperature, and then fed to the low temperature heat exchanger in heat exchange relationship with the weak solution derived from the absorber. Then the solution flows to the absorber which is cooled by cooling means. Thus, solution sprayed into the absorber absorbs the refrigerant vapor supplied from the evaporator, and provides a weak solution. This solution is further directed to the low temperature heat exchanger as described above.
In this manner, the two stage generator type absorption chiller is arranged such that the external heat supplied is utilized twice, once in the high and once in the low temperature generator, thus the thermal efficiency increases in comparison with the single effect type system.